The subject of the invention is a welding and backing ring for the connecting of two cylindrical enclosure parts of a flameproof enclosure of an electric cell (battery) having stacks of electrodes arranged symmetrically to the weld seam.
U.S. Pat. No. 4,546,054 and commonly assigned German Patent 3,520,854 disclose electric cell arrangements of the general type the present invention is directed toward improving.
Such electric cells are, for example, nickel hydrogen cells. They normally consist of a stack of electrodes which is surrounded by a flameproof, thin walled enclosure. In this case, the hydrogen is stored under high internal pressure (for example 60 bar). During discharging or charging of the cell, the hydrogen pressure decreases or increases, respectively, proportionally to the amount of charge taken or added. Due to these cyclical pressure fluctuations, the weld seam is subjected to a considerable load due to the pulsating internal pressure, it of course having to remain absolutely tight. The enclosure for such batteries consists of a flameproof cylindrical jacket which is made up of two enclosure halves joined by a radial connection welding. In order to prevent any damage to the stacks of electrodes by the welding heat, the weld seam is positioned such that, seen axially, it lies between two stacks of electrodes. The joining of the enclosure does not take place until the stacks of electrodes have been put in place; therefore, it must be reliably prevented that welding beads penetrate into the battery. For this purpose, the use of welding rings is known, which center the enclosure parts and cover the seam to be welded from the inside and thus prevent the penetration of welding beads into the enclosure. Since the welding ring is likewise welded to the enclosure during the welding of the enclosure halves, it additionally serves as radial reinforcement of the enclosure.
It is further known to use the welding ring additionally for holding the stacks of electrodes. For instance, the above-mentioned U.S. Pat. No. 4,546,054 discloses a welding ring for a symmetrical stack arrangement which has a T-shaped cross-section and is connected to inwardly directed metal plate rings. This welding/backing plate arrangement consists of three metal parts which fit well one into the other and consequently have to be fabricated with great accuracy. The construction is therefore expensive and relatively heavy. Because the metal plate rings are close to one another, if the cell is vibrated, for example during the rocket launch of a space capsule fitted with such a cell, there is a certain membrane effect, which can only be eliminated by relatively thick central insulating plates. This in turn increases the weight and makes the cells more expensive. In addition, due to the relatively close connection of the two stack halves, there is only a small thermal isolation, which can lead to problems.
The above-mentioned German Patent Specification 3,520,854 discloses a further embodiment of a welding ring which already has a means of holding the stacks of electrodes by tongue-shaped formations. Such cells are very suitable for conventional earth-bound applications. However, in testing under space travel conditions, such as occur for example during the launching of rockets, it has been found that the tongues can bend due to the vibrational forces occurring or that the stacks for their part vibrate, so that the destruction of the cells may ensue. The welding of the enclosure halves to each other and to the welding ring was carried out by the metal inert gas method (MIG). In this method, additional material is introduced to the weld location during welding via a welding wire. This has the advantage of a large weld upset formation, which contributes to the strength of the welded joint. There are, however, disadvantages in this method in the additional weight which is caused by the weld upset formation and is not justifiable in space deployment, and disadvantages on the other hand due to the fact that the upset is very inconvenient when fitting the cells in closely enclosing heat sinks.
The problem of introducing additional mass by the welding method can be avoided for example by carrying out the welding by the tungsten-inert gas method (TIG) or by plasma welding. These methods, however, require a much more accurate centering, in other words a more accurate concentricity and squareness of the enclosure parts and of the welding ring with respect to each other than in the case of the previously mentioned MIG welding method.
An object of the invention is to provide a welding and backing ring which has a high accuracy in terms of concentricity and squareness, which combines a high axial and radial strength or rigidity with low weight, which makes possible a high centering accuracy with respect to the stacks of electrodes and enclosure parts and which can be welded to the enclosure parts with small weld seam upset formation.
This object is achieved by providing a welding and backing ring which has a rectangular hollow profile section with an outwardly directed, approximately equatorially arranged collar.
The welding and backing ring is accordingly designed such that it has a rectangular hollow profile section with an outwardly directed, approximately equatorially arranged collar. Since the ring consequently represents a box profile, the wall thickness can be kept very thin. The equatorially arranged, outwardly directed collar serves on the one hand as stop for the enclosure halves of the cell enclosure and on the other hand as material supplier in the welding. The ring preferably consists of two identical rings which are connected mirror-invertedly and the meridian cross-section of which has a hat profile. These rings with hat profile may be made relatively simply from sheet metal by deep drawing. They are placed centrally one on the other and connected to each other, for example by welding, to form the box profile. To save weight and to facilitate the gas exchange within the cell, it is advantageous to provide the axially perpendicular areas of the ring with breakthroughs. These breakthroughs may be of circular or rectangular shape. In cases where requirements concerning the strength of the ring are relatively low, holes may also be made in the inner, axially parallel areas of the ring to save weight.
The wall thickness of the welding ring is to be dimensioned such that the welding ring achieves an optimum strength with lowest possible weight. Here of course the size of the flameproof enclosure also plays a part, and consequently the sheet thickness for the flameproof enclosure. It has been found that optimum results are achieved if the wall thickness of the welding ring is equivalent to approximately 50% of the wall thickness of the flameproof enclosure in the cylindrical region. The height of the welding ring in axial direction is to be equivalent to approximately 15 to 30 times, preferably approximately 20 times, the wall thickness of the welding ring. Furthermore, the radially measured width of the welding ring cross-section is to be approximately 5 to 20%, preferably approximately 10% of the enclosure diameter in the cylindrical region. The outwardly directed, approximately equatorially arranged collar is to protrude by approximately 3 times the wall thickness of the welding ring.
Other objects, advantages and noval features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.